Transfer assemblies for automatically moving individual workpiece's to subsequent die stations in a progressive die punch press forming machine are well known in the art. Typically, these prior art transfer assemblies include some form of engagement means for individually engaging the workpieces in their respective stations and then individually carrying the workpieces to the subsequent stations. One common and efficient method of driving the engagement means as it carries the workpieces to the next forming station is by a rocker arm type mechanism. That is, the engagement means is mechanically linked to the free swinging end of a rocker arm and displaced longitudinally of the forming stations as the rocker arm sweeps an arcuate path.
Examples of mechanical transfer assemblies having rocker arm mechanisms responsive to the press ram for moving the engagement means longitudinally of the die stations are shown in the U.S. Pat. No. 3,155,241 to Suofy, issued Nov. 3, 1964; U.S. Pat. No. 3,421,637 to Sofy, issued Jan 14, 1969; U.S. Pat. No. 4,198,854 to Sofy, issued Apr. 22, 1980; U.S. Pat. No. 4,436,199 to Baba et al, issued Mar. 13, 1984; and U.S. Pat. No. 4,513,602 to Sofy, issued Apr. 30, 1985.
The prior art transfer assemblies including engagement means moved by a rocker arm mechanism which is responsive to the press ram, such as those referenced above, are deficient in that the maximum obtainable indexing movement, i.e., movement equal to the distance between adjacent progressive die stations, is completely dependent upon the length of the rocker arm used and/or the degree of actuate oscillation thereof. Consequently, if the distance between adjacent die stations is very long, a long rocker arm is required to provide the necessary displacement or an average length rocker arm must sweep an unusually large arcuate path. Quite often it is impractical to provide a long rocker arm when attempting to achieve a long indexing movement due to the physical space limitations about the press. Similarly, a large arcuate sweep may be impossible due to the same space limitations about the press. Additionally, operating rocker arms and especially long rocker arms sweeping a large arcuate path present a danger to persons nearby unless adequately guarded with costly protective equipment. Further, as the length of a rocker arm increases, the greater, and more deleterious, the effect of resistance at the free swinging end becomes due to the leverage created. Similarly, as the degree of the arcuate path swept by the rocker arm increases, the mechanical advantage of the rocker arm, at certain positions, will decrease below an acceptable limit.